We wish to thank Georg Hasenkamp for valuable comments on an earlier draft of the manuscript and Steven Diamond for his kindness in reading the manu script and providing advice regarding the style of the exposition. We are also grateful to Miss Ingeborg Kasper for her careful typing of the manu script. Contents 1. Introduction 4 2. Price Indices Depending only on Prices 2. 1 Definition, Examples, Implications 4 2. 2 Characterizations of Pri e Indices 15 3. Price Indices Depending on Prices and Quantities 22 3. 1 Definition, Examples 23 3. 2 Fisher's System of Tests 29 3. 3 Implications and...

Among unconventional agents and unclassified viruses the contributions to this volume focused on prion-related diseases, with special emphasis on bovine spongiform encephalopathy and human spongiform encephalopathies, and Borna disease virus, an agent known since long time to be pathogenic for horses and sheep, which is now discussed as a potential pathogen for humans. Additionally, the volume contains articles about newly discovered viruses like porcine respiratory and reproductive syndrome virus and viruses that are classified only provisionally like African swine fever virus, hepatitis C...

Since the central theme of this book is the transmission of disease agents through the food chain, we will examine influenza viruses from this perspective. Influenza A viruses are found in humans, pigs, horses, sea mammals, and also in wild aquatic and domestic birds 23]. How are they spread? Between mammals, influenza is an airborne infection, but between birds, influenza can be either an airborne or waterborne infection. Influenza viruses of aquatic birds periodically transmit to domestic birds sometimes with catastrophic effects; this transmis sion can be either airborne or waterborne....